Solid delay line



l lvMay 31, 1966' EA'. BAUER I l 1 i l' f SOLID DELAY LINE I Y Filed March 18. 1953 ,2 @gets-Shout 1v V Y INVENTOR. .Paul A. Bquer ATTORNEY all RABAUE man 112mmuns $2.2 Sheet-seslllkeet 3 Filed uarcn 1a. 1.96:

rNvEmnR. Paul A. B auer ATTORNEY y 3,254,317 SQLID DELAY LINE Paul A. Bauer, Bradford, Pa., ussignor to Corning Glass Works, Coming, N.Y., a corporationof New York Filed Mar. 1 8, 1963, Ser. No. 265,752 4' Claims. (Cl. 333`30) This invention relates to asignal delay means and more particularly to a solid ultrasonic delay line and a method for attenuating spurious signals.- 5. Y

l Delay lines are used asdynamic storagedeviccs in electronic circuits.l One application fcr ultrasonic-delay lines is in the radar receiver art, for example, inmoving target identification (MIT) devices. lay line is used to delay received echoes or pulses for compatison with succeeding echoes or pulses in order 1to de tem-fine whether any change has occurred in thc timing of the signal. Another application is to provide for storage of energy pulses representing bits of information, such as binary digits or the like, in digital computors. By -means of suitable electrical circuitry, such delay lines gen- .erally termed digital delay lines, are fed said bits of information in a predetermined desired order, which bits are thereafter stored by recirculating them Vin said delay line for `any desired penod'of time, such as for example, until the particular bit or bits are required in the computing process, are removed, are replaced, or the like. Said bits of information generally represent binary digits and are fed to the delay line as pulses of direct currentv energy or are represented bythe lack of such pulses. This is contrasted to the inputsignal to ultrasonic dela-y lines,

such as those'used in MIT devices, where said input signals consist'of' continuous high frequency or pulse radio frequency energy; A

'An electrical signal is supplied to an ultrasonic delay line by means of a transducer mounted on the input facet of said delay line. In addition to producing the main signal, said transducer also produces other unwanted signals, herein termed spurious signals.- The utility of a solid ultrasonic delay line is greatly curtailed bythe number and ampiltude of such spurious signals, and here- Y tofore many attempts have been made to extend the utility ofsaid delay line by rejecting orattenuating these spurious signals, The more important considerations in rejecting or attenuating spurious signals are the reduction of the amplitude of individual spurious signals relative to the main signal, and the reduction of the vector sum of these signals, herein termed noise level. The noise level can be reduced by either reducing .the number of spurious signals of an lamplitude in excess of some desired amplitude sas determined by a particular application, or reducing the amplitude of the largest spurious signals. It should benoted that the main signal is caused to propagate through a delay medium to strike the reflecting facet at a predetermined desired fixed angle, herein termed strike angle, while the spurious signals naturally propagate at angles otherthan said fixed angle.

. It is an object of this invention to provide a solid ultrasonic delay line having a high' rate of utility.

-Another object of this invention is to'provide a solid In such devices, the de.'

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to strike .the reflection facets at angles less than said critical angle causing such spurious signals to be converted to a different mode of vibration towhich the output transducer of said 4delay line is substantially in sensitive, thereby cancelling or atte-nu'ating said spurious signals.

Additional objects, features and advantages of the pres ent invention will becomeapparent to those skilled in the art from the following detailed description and attached drawings on which, by way of'example, only `the pre ferred embodiments of this invention are illustrated.

FIGURE l is an oblique view of a solid ultrasonic delay line.

FIGURE 2 Vis a aiagmnmanc illustration er the path,

of a beam Aof elastic waves Vpropagating through the solid Ultrasonic delay line of FIGURE I in accordance with this invention.

FIGURE 3- is a diagrammatic view of the opout" l i pattem ofthe path of `elastic waves and the spurious signals associated therewith in astandard delay line.

FIGURE 4 is a diagrammatic view of the filopout".

t pattern ofthe path of elastic waves and .the spurious signals associated therewith in a delayline formed in accordance with this invention.

FIGURE 5 isa diagrammatic illustration of the pathA of a beam of elastic waves propagating through a solid ultrasonic delay line wherein the spurious signals on both sides of the main signal are .attenuated by mode conversion.

FIGURE 1 illustrates a solid 'ultrasonic delay line as'- scmbly wherein delay `medium 10 has input facet 12, output facet 14, and reflection facets 16, 18, 20 and 22 formed thereon. Input transducer 24 :is shown mounted on input facet 12, and output transducer 26 is shownv mounted on output facet 14. Acoustic tbsorbers-ZS are mounted about the periphery of said delay line medium at predetermined positions as ,hereinafter-described to absorb certain spurious signals.

with conventional delay medium .ultrasonic delay line having improved cancellation or l rejection of selected individual spurious signals.

Still another object of this invention is fto provide a solid ultrasonic delay line having'improved main signal to noise level ratio.

Suitable delay lineme'dium materials 'are fused silica, alkali-lead-silicate glass such as described in co-pendingv patent application by'H. L. Hoover and M f E. Nordberg, S.N. 118,185, filed June I9, 19 6l,"and' the like Although the speci-fic peripheral configuration of the digital ultrasonic'delay line medium in accordance lwith this invention is not critical,exoept as hereinafter noted I in 4connection with the forming of input, output, and signal reflection facets, the medium must be of a flat type. The blank for such a,` delay medium may be. either 'molded 'in .a desired shape or cut from a large shaped blank in accordance with conventional delay medium forming procedures, and may then be annealed inaecordanoe The blank, is then ground and polished as desired.

Transducers 24 and 26 may be composed of a crystalline piezoelectric 4material, such as crystalline quartz, barium tit'anate, mixtures of'le'ad .zirc'onate and lead tita'nate, potassium sodium niobat, and the lke. are -sealed to facets 12 and l'4nrenspectively on delay medium 10. Acoustic absorber 28 may be composed of any acoustic absorbing material Asuch aslead, tin. and

the like, and the lcompositionis not critical as long as the material can be bonded to the delay medium and has a high signal attenuation. A particularly suitable absorber material is an indium rich alloy comprising about 60 percent' indium and about 40 percent tin.

annealing practices.y

They

Paten't'edMaySl, 1966 v Ina solid ultrasonic delay line, an elastic wave, vibrating in the thicknessshear mode, is completely reflected l from any interface or reflecting surface if it Strikes the reflecting surface at some angle greater than the critical 'angle of the delay medium. If the wafve strikes at an l angle less than the critical, it is at least in part converter! after dispersed, eliminated or attenuated.

The reflected signal path pattern can be illustrated by a 't longitudinal orvcompressional waves, which are therev tlopout as shown in FIGURES 3 and. 4. vFIGURE 3 illustrates a opout of a solid ultrasonic delay line hav in'g a regular rectangular fonn. The main signal'is illustrated by line 30 having a `strike angle denoted by a. The area encompassed by angles A and Brillustrates the spuri' '.ous signals; In a regular rectangular solid delay line,

angles A and B will be substantially equal to each other and to the difference between the critical angle of the delay medium andthe ,signal strike angle. In such a delay line, strike angle a is gene-rally 45 degrees.

Referring now to FIGURES Zand .4, it has been discovered'that by causing the main signal, illustrated by line 32, to have a strike angle a' ranging from the critical angle to about 2 degrees more than the critical angle of the delayI medium, about one-half of the spurious-signals closest to the main signal are caused to have a strike angle less than the-critical angle of said delay medium. Such spurious signalsA are then converted from shear elastic waves to IOngitudinaland compressional waves eliminating or attenuating said spurious signals. The only spurious signals remaining on one side of the main signal are illustrated by the area of angle C. Since the spurious signals represented by the area of angle C are substantially zero, the only significant spurious signals remaining are those illustrated by the area of angleD which are substantiallyone-half of the spurious signals of heretofore known delay lines suchv as that illustrated in FIGURE@ Y Referring now to FIGURE 5, it isseen that by varying the peripheral geometry of the-delay medium it is possible to 4cause spurious signals, illustrated by the area of angle E, which substantially correspond to those illustrated by the area of angle D in FIGURE 4, subsequently strike a reflecting facet at an' angle such'aa F forexample, which is less than thecritical iangle, thereby causing these remaining spurious signals to be converted from shear elastic waves to longitudinal or .compressonal waves ,and .consequently be rejected-or attenuated as heretofore described. Y

A typical example of carrying out this, .invention is illus' l trated in FIGURES 2 and 4 and they following description.

A delay medium of an -alkali-lead-silicat`e glass, such as described in the heretofore noted Hoover-Nordberg patent application, which glass has a criticalangle of about 39 degrees, may be suitably formed int-o a rectangular platetype` configuration. Signal input and output facets are formed at adjacent c orn'ers of said plate and are so positioned that the signal strike angles at the reflection facets would be 39 degrees 30. minutes. The plate is then polished to substantially a commercial plate glass polish on the maior plane surfaces, reflection facets, and input and output facets with ce'rium oxide having one-half to one micron size. A

lnputand output transdi'reersofA crystalline quartz, A.C. cut, are formed and mounted on said input and output fcets for thickness-shear mode vibration parallel to the major pl'anesof said delay medium. Y

Acoustic absorbers are formed of the heretofore noted indium rich alloy and-are mounted on the reflection facets between theareas where the main signal will strike and be reflected, such as is illustrated in FIGURE 1. TheA various signals which are not converted to a different mode of vibration as heretofore described are absorbed by said .acoustic absorbers.

In the delay line of this example, the spurious signals were 28 db below the main signal level, which'is an its strike angle at the reflection facets is about 39 degrees -I 30 minutes', and acoustic absorbers adhered to said retleci improvement of' approximately 19 db `-over heretofore y Y i Aknown delay line configurations.

A solid ultrasonic delay line produced in accordance v with this invention will have improved cancellation of- Ascope of the invention except insofar as set forth in the,A

following claims.

What is claimed is:

1. An ultrasonic delay 4line comprising a soliddelay medium in the form of a flat -plate having input, output and reflection facets formed on the periphery thereof, the flat surfaces of said plate comprising the maior'planes of said delay medium, signal input and ,output transducers mounted on said input and output facets respectively' for vibration in the thicknessshear'fmode 'parallel to said maior planes, said 'input and output transducers being substantially insensitive -to waves vibrating in the compressional mode, said reflect-ion facets vbeing formed and 'said input and output transducers being mounted to facets and substantially ther-balance of the spurious signals have a strike angle less than thec'ritical angle at at least one other of `the reflection facets, and acoustic absorbers adhered to said reflection :facets-between points of reflection .of said main signal.

2. The ultrasonic delay line 4of claiml 1- wherein said delay medium is formedvof material selected from fthe group consisting of fused silica and alkali-leadsilicate glass. Y v3. 'lfhe ultrasonic delay line of claim 1 wherein said input and output .transducers are 'formed of material selected from the groupconsisting 'of crystalline quartz, barium titanate, potassium sodium niobate, and mixtures of lead'zirconate an'd lead titanate. 4. An ultrasonic delay line comprising a solid ..lay

medium of alltali-lead-silicate glass in theform of a flat plate having input, output, and reflection facets formed on the periphery thereof, the flat surfaces of said plate comprising the major planes of said delay medium, signal input and output yquartz transducers mounted -on said input and output facets respectively for vibration in the thicknessshear mode parallel -to said maior planes, said input ,and output transducers being substantially insensitive to waves vibrating in the compressional mode and being mounted to propagate the main signal wave so that tion facet between points of reflection of said :nain signal.

References Cited-by the Examiner UNITED STATES PATENTS HERMAN KARL' SAALBACH, Pfimmy Examiner. c. Bauart?, Assistant examiner.

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4. AN ULTRASONIC DELAY LINE COMPRISING A SOLID DELAY MEDIUM OF ALKALI-LEAD-SILICATE GLASS IN THE FORM OF A FLAT PLATE HAVING INPUT, OUTOUT AND REFLECTION FACETS FORMED ON THE PERIPHERY THEREOF, THE FLAT SURFACES OF SAID PLATE COMPRISING THE MAJOR PLANES OF SAID DELAY MEDIUM, SIGNAL INPUT AND OUTPUT QUARTZ TRANSDUCERS MOUNTED ON SAID INPUT AND OUTPUT FACETS RESPECTIVELY FOR VIBRATION IN THE THICKNESS-SHEAR MODE PARALLEL TO SAID MAJOR PLANES, SAID INPUT AND OUTPUT TRANSDUCERS BEING SUBSTANTIALLY INSENSITIVE TO WAVES VIBRATING IN THE COMPRESSIONAL MODE AND BEING MOUNTED TO PROPAGATE THE MAIN SIGNAL WAVE SO THAT ITS STRIKE ANGLE AT THE REFLECTION FACETS IS ABOUT 39 DEGREES 30 MINUTES, AND ACOUSTIC ABSORBERS ADHERED TO SAID REFLECTION FACET BETWEEN POINTS OF REFLECTION OF SAID MAIN SIGNAL. 